Elastomeric copolymer of ethylene

ABSTRACT

Elastomeric ethylene/propylene or ethylene/propylene/polyene copolymers containing small amounts of one or more alpha-olefins are prepared by a slurry process wherein the polymerization reaction is carried out in a mixture of liquid propylene and alpha-olefin.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. Ser. No. 08/825,660 filed Apr.3, 1997 now U.S. Pat. No. 6,046,287 which is a continuation of U.S. Ser.No. 08/304,498 filed Sep. 12, 1994, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a process for the preparation ofethylene-based copolymers and, more particulary, it relates to a slurryprocess for the preparation of elastomeric copolymers of ethylene.

2. Description of the Prior Art

Among the ethylene-based elastomeric copolymers, only ethylene-propylene(EPM) and ethylene-propylene-diene (EPDM) elastomers are produced on acommercial scale, at the date of the present invention.

The industrial production of EPM and EPDM elastomers is currentlycarried out in the presence of Ziegler-Natta vanadium-based catalysts,by solution or slurry processes.

In the solution processes the comonomers are dissolved in a solvent,generally hexane, in which the formed polymer is soluble. In the slurryprocesses the reaction medium is essentially constituted by liquidolefins and the polymer is formed as a precipitate suspended in theliquid phase.

A slurry process offers a number of advantages over a solution process,namely:

no stirring viscosity problems;

very homogeneous reaction medium;

easier removal of the reaction heat;

increased reactor throughput owing to higher concentration of thepolymer in the medium;

higher polymerization yields;

capability of producing very high MW polymers;

energy savings for the recovery of the polymer;

lower investment and production costs.

However, a major problem of a slurry process arises from the adhesiveproperties of the rubbery material. As a matter of fact, the solidparticles of the polymer have a tendency to stick to one another or tothe wall surface and to the agitating element of the reactor. Thisworsens to a large extent the diffusion of ethylene in the reactionmedium and, what is more, causes intensive fouling of the reactor, thusrendering the preparation of the polymer very difficult.

In order to avoid such problems, a solvent, such as toluene orcyclohexane, can be added to the reaction medium, which acts both asantifouling agent and as vehicle of the catalyst system. The use of alow boiling diluent, such as propane, has also been proposed. As aresult, however, the above indicated advantages of a slurry process aredrastically decreased.

Another solution which has been proposed to render the process in bulkpossible, is the addition of antistatic agents into the polymerizationreactor. This solution, however, is not completely satisfactory and,moreover, has the drawback of introducing undesired compounds in thefinal product.

Recently, processes have been disclosed for the preparation ofelastomeric ethylene-based copolymers in the presence ofmetallocene/alumoxane catalysts.

European patent application No. 347,128 discloses a process forproducing an ethylene/α-olefin elastomer in slurry polymerization,utilizing a zirconocene/alumoxane catalyst supported on a silica gelsupport. The examples relate to the preparation of ethylene/propylenecopolymers in liquid propylene. It is said that, unless the supportedcatalyst is prepolymerized with ethylene or another α-olefin beforebeing used in the slurry polymerization process, the reactor foulinginvariably occurs to a very large extent.

In European patent application No. 535,230, a slurry polymerizationprocess for preparing an ethylene-based copolymer has been proposed,which prevents the occurence of fouling. This process is carried out inthe presence of both a polysiloxane additive and a silica gel supportedzirconocene/methylalumoxane catalyst. All of the examples relate toethylene/propylene elastomers. In the comparative examples in which nopolysiloxane additive has been used, clogging and jamming have beenobserved.

In International patent application PCT/EP93/01528, there is described aprocess for the preparation of ethylene/1-butene orethylene/1-butene/diene elastomeric copolymers in the presence of ametallocene catalyst, wherein the reaction medium is substantiallyconstituted of liquid 1-butene. This process is free of foulingphenomena of the reactor.

SUMMARY OF THE INVENTION

It has now unexpectedly been found that it is possible to prepareethylene/propylene or ethylene/propylene/polyene elastomeric copolymers,containing small amounts of one or more alpha-olefins, by means of aslurry process, free of fouling phenomena of the reactor, wherein thereaction medium is substantially constituted of a mixture of liquidpropylene and alpha-olefin, without resorting to supporting and/orprepolymerization treatments of the catalyst.

Therefore, it is an object of the present invention a process for thepreparation of an elastomeric copolymer of ethylene, comprising theslurry polymerization reaction of a mixture comprising ethylene,propylene, at least 15% by weight of at least one alpha-olefin offormula (I):

CH₂═CHR  (I)

wherein R is an alkyl radical containing from 2 to 10 carbon atoms and,optionally, small amounts of at least one polyene, in a reaction mediumwhich essentially consists of liquid propylene and alpha-olefin togetherwith the dissolved gaseous ethylene, in the presence of anon-prepolymerized catalyst based on a metallocene compound of atransition metal belonging to the Group IIIb, IVb, Vb, VIb and ofLanthanides of the Periodic Table of the Elements.

Another object of the present invention is an elastomeric copolymer ofethylene with propylene, at least one alpha-olefin and, optionally, witha polyene, obtainable with the process of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Catalysts suitable to be used in the process of the present inventionare, for example, those comprising the product obtained by contacting:

(A) a metallocene compound of formula (II)

(C₅R¹ _(5−m))R² _(m)(C₅R¹ _(5−m)) MQ₂  (II)

 wherein

M is Ti, Zr, Hf or V; the C₅R¹ _(5−m) groups, same or different, arecyclopentadienyl rings equally or differently substituted;

R¹, same or different, are hydrogen atoms or alkyl, alkenyl, aryl,alkylaryl or arylalkyl radicals containing from 1 to 20 carbon atoms,which can also contain Si or Ge atoms, or Si(CH₃)₃ groups, or also twoor four substituted R¹ of a same cyclopentadienyl group can form one ortwo rings having from 4 to 6 carbon atoms;

R² is a group bridging the two cyclopentadienyl rings and is selectedfrom CR³ ₂, C₂R³ ₄. SiR³ ₂, Si₂R³ ₄, GeR³ ₂, Ge₂R³ ₄, R³ ₂SiCR³ ₂, NR¹and PR¹, wherein R³, same or different, are defined as R¹ or two or foursubstituents R³ can form one or two rings having from 3 to 6 carbonatoms;

Q, same or different, are halogen atoms, hydrogen atoms, R¹, OR¹, SR¹,NR¹ ₂ or PR¹ _(2;)

m can be 0 or 1; optionally pre-reacted with an organometallic compoundof aluminum of formula (III):

AlR⁴ _(3−z)H_(z)  (III)

 wherein R⁴, same or different, are alkyl, alkenyl or alkylaryl radicalscontaining from 1 to 10 carbon atoms, and z can be 0 or 1; and

(B) an alumoxane, optionally in admixture with an organometalliccompound of aluminum of formula (III):

AlR⁴ _(3−z)H_(z)  (III)

 wherein R⁴ and z are defined as above, or one or more compounds able togive a metallocene alkyl cation.

In the case in which m=0, particularly suitable cyclopentadienylcompounds are those in which the C₅R¹ _(5−m) groups arecyclopentadienyl, pentamethyl-cyclopentadienyl, indenyl or4,5,6,7-tetrahydroindenyl groups, and substituents Q are chlorine atoms,C₁-C₇ hydrocarbyl groups, preferably methyl or hydroxyl groups.

Non limitative examples of cyclopentadienyl compounds of general formula(II), wherein m=0, are:

(Cp)₂MCl₂ (MeCp)₂MCl₂ (BuCp)₂MCl₂ (Me₃Cp)₂MCl₂ (Me₄Cp)₂MCl₂ (Me₅Cp)₂MCl₂(Me₅Cp)₂MMe₂ (Me₅Cp)₂M(OMe)₂ (Me₅Cp)₂M(OH)Cl (Me₅Cp)₂M(OH)₂(Me₅Cp)₂M(C₆H₅)₂ (Me₅Cp)₂M(CH₃)Cl (EtMe₄Cp)₂MCl₂ [(C₆H₅)Me₄Cp]₂MCl₂(Et₅Cp)₂MCl₂ (Me₅Cp)₂M(C₆H₅)Cl (Ind)₂MCl₂ (Ind)₂MMe₂ (H₄Ind)₂MCl₂(H₄Ind)₂MMe₂ {[Si(CH₃)₃]Cp}₂MCl₂ {[Si(CH₃)₃]₂Cp}₂MCl₂ (Me₄Cp)(Me₅Cp)MCl₂(Me₅Cp)MCl₃ (Me₅Cp)MBenz₃ (Ind)MBenz₃ (H₄Ind)MBenz₃ (Cp)MBu₃ (Me₅Cp)MCl(Me₅Cp)MH

wherein Me=methyl, Et=ethyl, Bu=butyl, Cp=cyclopentadienyl, Ind=indenyl,H₄Ind=4,5,6,7-tetrahydroindenyl, Benz=benzyl, M is Ti, Zr, Hf or V,preferably it is Zr.

In the case in which m=1, particularly suitable cyclopentadienylcompounds are those wherein groups C₅R¹ _(5−m) are cyclopentadienyl,indenyl, 2-methyl-indenyl, 4,7-dimethyl indenyl,2,4,7-trimethyl-indenyl, 4,5,6,7-tetrahydroindenyl,2-methyl-4,5,6,7-tetrahydroindenyl,4,7-dimethyl-4,5,6,7-tetrahydroindenyl,2,4,7-trimethyl-4,5,6,7-tetrahydroindenyl or fluorenyl groups, R² is adivalent group (CH₃)₂Si, C₂H₄ or C(CH₃)₂, and substituents Q arechlorine atoms or C₁-C₇ hydrocarbyl groups, preferably are methylgroups.

Non limitative examples of cyclopentadienyl compounds of general formula(II), wherein m=1, are:

Me₂Si(Me₄Cp)₂MCl₂ Me₂Si(Me₄Cp)₂MMe₂ Me₂C(Me₄Cp) (MeCp)MCl₂Me₂Si(Ind)₂MCl₂ Me₂Si(Ind)₂MMe₂ Me₂Si(Me₄Cp)₂MCl(OEt) C₂H₄(Ind)₂MCl₂C₂H₄(Ind)₂MMe₂ C₂H₄(Ind)₂M(NMe₂)₂ C₂H₄(H₄Ind)₂MCl₂ C₂H₄(H₄Ind)₂MMe₂C₂H₄(H₄Ind)₂M(NMe₂)OMe Ph(Me)Si(Ind)₂MCl₂ Ph₂Si(Ind)₂MCl₂Me₂C(Flu)(Cp)MCl₂ C₂H₄(Me₄Cp)₂MCl₂ C₂Me₄(Ind)₂MCl₂ Me₂SiCH₂(Ind)₂MCl₂C₂H₄(2-MeInd)₂MCl₂ C₂H₄(3-MeInd)₂MCl₂ C₂H₄(4,7-Me₂Ind)₂MCl₂C₂H₄(5,6-Me₂Ind)₂MCl C₂H₄(2,4,7-Me₃Ind)₂MCl₂ C₂H₄(3,4,7-Me₃Ind)₂MCl₂C₂H₄(2-MeH₄Ind)₂MCl₂ C₂H₄(4,7-Me₂H₄Ind)₂MCl₂ C₂H₄(2,4,7-Me₃H₄Ind)₂MCl₂Me₂Si(2-MeInd)₂MCl₂ Me₂Si(3-MeInd)₂MCl₂ Me₂Si(4,7-Me₂Ind)₂MCl₂Me₂Si(5,6-Me₂Ind)₂MCl Me₂Si(2,4,7-Me₃Ind)₂MCl₂ Me₂Si(3,4,7-Me₃Ind)₂MCl₂Me₂Si(2-MeH₄Ind)₂MCl₂ Me₂Si(4,7-Me₂H₄Ind)₂MCl₂Me₂Si(2,4,7-Me₃H₄Ind)₂MCl₂ Me₂Si(Flu)₂MCl₂ C₂H₄(Flu)₂MCl₂

wherein Me=methyl, Cp=cyclopentadienyl, Ind=indenyl, Flu=fluorenyl,Ph=phenyl, H₄Ind=4,5,6,7-tetrahydroindenyl, M is Ti, Zr, Hf or V,preferably it is Zr.

Another family of compounds of a transition metal useable in thecatalyst according to the present invention are the monocyclopentadienylcompounds of the “constrained geometry” type described in U.S. Pat. No.5,055,438, the content of which is incorporated in the presentdescription. Other useful “constrained geometry” monocyclopentadienylcompounds include those having the formula:

wherein M is titanium or zirconium; Cp is a cyclopentadienyl group orderivative thereof that is π-bound to M and substituted at least by Z; Zis a divalent moiety comprising oxygen, sulfur, boron, or a member ofGroup 14 of the Periodic Table of Elements; Y is a ligand groupcomprising nitrogen, phosphorous, oxygen or sulfur, or optionally Z andY together form a fused ring system; X, independently each occurrence ishydride or a hydrocarbyl, silyl or gennyl group having up to 20 carbon,silicon or germanium atoms; and A is an anion of a Lewis acid, A, havingrelative Lewis acidity greater than or equal to that of phenylbis(perfluorophenyl) borane, said anion being compatible with the metalcation. As used herein, “constrained geometry” means that the metal atomis forced to greater exposure of the active metal site because one ormore substituents on the substituted delocalized π-bondedcyclopentadienyl group forms a portion of a ring structure including themetal atom, wherein the metal is both bonded to an adjacent covalentmoiety and held in association with the substituted delocalized η-bondedcyclopentadienyl group though an η⁵ or other π-bonding interaction. Eachrespective bond between the metal atom and the constituent of thesubstituted delocalized π-bonded cyclopentadienyl group need not beequivalent. That is, the metal may be symmetrically or unsymmetricallyπ-bound to the substituted delocalized π-bonded cyclopentadienyl group.

Organo-metallic compounds of aluminum useable in the catalyst accordingto the present invention are, for example, linear, branched or cyclicalumoxanes, containing at least one group of the type (IV):

wherein substituents R⁴, same or different from each other, are R¹ or agroup —0—Al(R⁴), and, optionally, some R⁴ can be halogen or hydrogenatoms.

In particular, it is possible to use alumoxanes of formula (V):

in the case of linear compounds wherein n=0 or an integer comprisedbetween 1 and 40, or alumoxanes of formula (VI):

in the case of cyclic compounds wherein n is an integer comprisedbetween 2 and 40.

Radicals R¹ are preferably methyl, ethyl, isobutyl. Examples ofalumoxanes suitable to be used according to the present invention aremethylalumoxane (MAO) and tetraisobutyldialumoxane (TIBAO).

A particular class of organometallic compounds of aluminum useable inthe catalyst according to the invention is that of the compoundsobtainable by reaction of aluminum alkyls or alkylhydrides with water,in molar ratio comprised between 1:1 and 100:1 respectively. Compoundsof this type are described in European patent application EP-575 875,the content of which is incorporated in the present description.

Organometallic compounds of aluminum also useable in the catalystaccording to the invention are those of formula (VII)

or of formula (VIII)

wherein R¹ is defined as above.

The molar ratio between the aluminum and the metal of the metallocenecompound is generally comprised between about 10:1 and about 10000:1,and preferably between about 100:1 and about 5000:1.

Non limitative examples of compounds able to give a metallocene alkylcation are compounds of formula Y⁺Z⁻, wherein Y+ is a Brbnsted's acid,able to give a proton and to react irreversibly with a substituent Q ofthe compound of formula (II) and Z⁻ is a compatible anion, which doesnot coordinate, able to stabilize the active catalytic species whichoriginates from the reaction of the two compounds, and which issufficiently labile to be displaced from an olefinic substrate.Preferably the anion Z⁻ comprises one or more boron atoms. Morepreferably, the anion Z⁻ is an anion of formula BAr⁽⁻⁾ whereinsubstituents Ar, same or different from each other, are aryl radicalssuch as phenyl, pentafluorophenyl, bis(trifluoromethyl)phenyl.Particularly preferred is the tetrakis-pentafluorophenylborate.Furthermore, compounds of formula BAr₃ can be suitably used. Compoundsof this type are described, for example, in the published Internationalpatent application W092/00333, the content of which is incorporated inthe present description.

The catalysts used in the process of the present invention can be alsoused on inert supports. This is obtained by depositing the metallocenecompound (A), or the product of the reaction of the same with thecomponent (B), or the component (B) and subsequently the metallocenecompound (A), on inert supports such as for example silica, alumina,styrene-divinyl benzene copolymers or polyethylene.

A particular class of porous organic supports which may be used arepolymers with functional groups having active hydrogen atoms and thefollowing characteristics:

A porosity (B.E.T.) generally higher than 0.2 cc/g, preferably higherthan 0.5 cc/g, more preferably higher than 1 cc/g. In particular,supports suitably useable have a porosity between 1 and 3 cc/g.

A surface area (B.E.T.) generally higher than 30 m²/g, preferably higherthan 50 m²/g, more preferably higher than 100 m²/g. In particular, thesurface area can reach values of about 500 m²/g and over.

The organic support is preferably in the form of particles havingcontrolled morphology, in particular microspheroidal morphology with adiameter comprised between 5 and 1000 μm, perferably between 10 and 500μm, more preferably between 20 and 200 μm.

Examples of suitable functional groups are hydroxyl groups, primary andsecondary amino groups, sulphonic groups, carboxylic groups, amidogroups, N-monosubstituted amido groups, sulphonamido groups, sulphydrilgroups, imido groups and hydrazido groups.

The amount of functional groups contained in the porous organic supportsis generally higher than 0.2 milliequivalents (meq) for each gram ofsolid support, preferably higher than 0.5 meg for each gram of solidsupport, more preferably is between 1 and 6 meq for each gram of solidsupport.

Particularly suitable porous organic supports can be obtained frompartially cross-linked porous styrenic polymers. These supports can beprepared by copolymerization of styrenic monomers, such as styrene,ethylvinylbenzene, vinyltoluene, methylstyrene and mixtures thereof,with comonomers able to be cross-linked, such as divinylbeizene,divinyltoluene and mixtures thereof. Preferred sytrenic polymers arepartially cross-linked styrene/divinylbeizene copolymers. Methods forthe preparation of these copolymers are described, for example, in U.S.Pat. No. 4,224,415. Porous polymers of this type can be functionalizedby means of known methods. The most common methods to functionalizepolystyrene resins are reported in “Comprehensive Pol. Sci., PergamonPress, pages 82-85 (1989)”.

Functionalized porous sytrenic polymers useable as supports can also bedirectly obtained from the copolymerization of styrenic monomers withcomonomers functionalized groups containing active hydrogens or theirprecursors.

The components of the catalyst can be contacted among them before thepolymerization. The contact time is generally comprised between 5 and 20minutes.

According to a particular example of embodiment, the process of thepresent invention is carried out in a mixture of liquid propylene and1-butene, in the presence of a catalyst which comprises the product ofthe reaction between:

(A) ethylene-bis(4,5,6,7-tetrahydroindenyl)zirconium dichloride, and

(B) a compound selected from tetraisobutyl-dialumoxane (TIBAO) and theproduct of the reaction between aluminum triisobutyl (TIBAL) and water.

In this case the amounts by weight of 1-butene in liquid phase aregenerally comprised between 15% and 90% and, preferably, between 20% and50%. The amounts by weight of ethylene dissolved in the reaction mixtureare generally comprised between 8% and 45% and, preferably, between 0and 5%. The optional amount by weight of diene is generally comprisedbetween 0 and 5%. The balance to 100% consists of liquid propylene.

The polymerization process of the present invention can be carried outeither discontinuously or continuously.

The polymerization temperature is generally comprised between 0° C. and200° C., in particular between 20° C. and 100° C., and more particularlybetween 30° C. and 80° C.

The polymerization yields depend on the purity of the metallocenecomponent of the catalyst. Therefore, the metallocene compounds obtainedby the process of the invention can be used as such or subjected topurification treatments.

In particular, by the process of the present invention it is possible toprepare elastomeric copolymers of ethylene containing from 35% to 85%,preferably from 60% to 80%, by moles of ethylene units, from 10% to 65%,preferably from 15% to 50%, by moles of units deriving from propyleneand from at least one alpha-olefin of formula (I):

CH₂═CHR  (I)

wherein R is defined as above, and from 0 to 5%, preferably from 0 to3%, by moles of units deriving from a polyene, having the followingcharacteristics:

product of reactivity ratios r_(e)·r_(α)lower than 1 and, preferably,lower than 0.8;

less than 2%, preferably less than 1%, of CH₂ groups in the chaincontained in sequences (CH₂)_(n), wherein n is an even integer;

intrinsic viscosity higher than 0.2 dl/g.

The analysis of the distribution of the comonomeric units has beencarried out by ¹³C-NMR analysis. The assignements have been carried outas described by the following articles:

M. Kakugo et al., Macromolecules 15, 1150-1152 (1982);

L. Sun, S. Lin, J. Polym. Sci.- Part A-Polym. Chem. 28, 1237, (1990);

E.T. Hsieh, J. C. Randall, Macromolecules 15, 353 (1983);

H.N. Cheng, J. Polym. Phys. 21, 573, (1983).

The product of reactivity ratios r_(e)·r_(α), wherein r_(e) is thereactivity ratio of ethylene and r_(α)the reactivity ratio of thecomonomeric units, is calculated, in the case ofethylene/propylene/1-butene terpolymers, according to the followingformula:

r_(e)·r_(α)=4(EE)(PP+BB)/(EP+EB)²

wherein EE, PP, BB, EP and EB represent respectively the sequencesethylene/ethylene, propylene/propylene, butene/butene,ethylene/propylene and ethylene/butene.

The alpha-olefins of formula (I) useable in the process of the presentinvention, for example, 1-butene, 1-pentene, 1-hexene,4-methyl-1-pentene, allyl-trimethyl-silane, 1-butene being preferred.

Polyenes useable comprise:

polyenes able to give unsaturated units, such as:

linear, non-conjugated dienes such as 1,4-hexadiene trans, 1,4-hexadienecis, 6-methyl-1,5-heptadiene, 3,7-dimethyl-1,6-octadiene,11-methyl-1,10-dodecadiene;

monocyclic diolefins such as, for example, cis-1,5-cyclo-octadiene and5-methyl-1,5-cyclooctadiene;

bicyclic diolefins such as for example 4,5,8,9-tetra-hydroindene and 6and/or 7-methyl-4,5,8,9-tetrahydro-indene;

alkenyl or alkyliden norbornenes such as for example,5-ethyliden-2-norbornene, 5-isopropyliden-2-norbornene,exo-5-isopropenyl-2-norbornene;

polycyclic diolefins such as, for example, dicyclopenta-diene,tricyclo-[6.2.1.0^(2.7)]4,9-undecadiene and the 4-methyl derivativethereof;

non-conjugated diolefins able to cyclopolymerize, such as 1.5-hexadiene,1,6-heptadiene, 2-methyl-1,5-hexadiene;

conjugated dienes such as butadiene and isoprene.

Copolymers in which the content of units deriving from ethylene is nearthe upper limit of 85% by mol., have melting enthalpies which can behigher than 20 J/g.

From the process of the invention copolymers with intrinsic viscosityhigher than 2.0 dl/g and, preferably, higher than 3.0 dl/g can beobtained. The intrinsic viscosity can reach values of 4.0 dl/g and over.

Generally, the above mentioned copolymers result endowed with closedistribution of the molecular weights. An index of the molecular weightdistribution is represented by the ratio M_(w)/M_(u) which, for thecopolymers of the invention, is generally lower than 3.5 and, morepreferably, lower than 3.

The molecular weight distribution can be changed using mixtures ofdifferent metallocene compounds, or carrying out the polymerization inseveral steps differing as to the polymerization temperatures and/or theconcentration of the molecular weight regulator.

The structure of the above mentioned copolymers results to be highlyregioregular. In fact, by the ¹³C-NMR analysis signals relating to(CH₂), sequences, wherein n is an even integer are not generallydetectable.

The above mentioned copolymers are generally soluble in common solventssuch as, for example, hexane, heptane and toluene.

The elastomeric copolymers obtainable by the process of the presentinvention are characterized by valuable properties, such as the lowcontent of ashes and the uniformity of the distribution of thecomonomers in the copolymeric chain.

These copolymers can be vulcanized using the formulations and methodsknown for EPM and EPDM rubbers, working for example in the presence ofperoxides or sulphur. Rubbers endowed with valuable elastomericproperties are obtained.

Rubbers obtained from these copolymers can be transformed inmanufactured articles by the generally used working processes forthermoplastic materials (moulding, extrusion, injection, etc.). Theobtained manufactured articles are endowed with interesting elasticproperties and are used in all the applications typical for thealpha-olefinic elastomers.

In particular the products obtained from copolymers having a highcontent of ethylene units can be advantageously used as coatings forwires and cables.

The following examples are given to illustrate and not to limit theinvention.

CHARACTERIZATIONS

The propylene and alpha-olefin content in the copolymer were determinedby ¹³C-NMR analysis.

The ¹³C-NMR analysis of the copolymers were carried out by a BrukerAC200 instrument, at a temperature of 120° C., on samples prepareddissolving about 300 mg of the polymer in 2.5 cc of a 3:1trichlorobenzene/C₂D₂Cl₄ mixture. Spectra were recorded with thefollowing parameters:

Relaxation delay =12 seconds

Number of scannings =2000:2500

The intrinsic viscosity [] was measured in tetrahydronaphthalene at 135°C.

Measures of Differential Scanning Calorimetry (D.S.C.) were carried outon an instrument DSC-7 of Perkin Elmer Co. Ltd., according to thefollowing method. About 10 mg of sample obtained from the polymerizationwere cooled to −25° C. and thereafter heated at 200° C. with a scanningspeed corresponding to 10° C. minute. The sample was kept at 200° C. for5 minutes and thereafter cooled with a scanning speed corresponding to10° C./minute. Then, a second scanning was carried out according to thesame modalities of the first one. The values reported are those obtainedin the first scanning.

The distribution of molecular weights was determined by GPC carried outon an instrument WATERS 150 in orthodichlorobenzene at 135° C.

PREPARATION OF THE CATALYTIC COMPONENTSEthylene-Bis(4,5,6,7,-Tetrahydroindenyl)Zirconium,Dichloride

Was prepared according to the method described by H. H. Brintzinger etal. in “J. Organometal. Chem., 288, Page 63, (1985).”

Methylalumoxane (Mao)

A commercial product (Schering, MW 1400) in 30% by weight toluenesolution was used. After having removed the volatile fractions undervacuum, the vitreous material was ground until a white powder wasobtained and this was further treated under vacuum (0.1 mmHg) for 4hours at a temperature of 40° C. The powder thus obtained shows goodflowing characteristics.

POLYMERIZATIONS EXAMPLES 1-3

Into a 4.25 litre autoclave, provided with stirrer, mano-meter,temperature indicator, catalyst supplying system, lines for supplyingthe monomers and thermostating jacket, degased by washing with ethyleneat 80° C., the amounts of water, ethylene, propylene and 1-buteneindicated in Table 1 were introduced at room temperature. The autoclavewas then heated at a temperature 5° C. below the polymerizationtemperature. The solution of the catalyst was prepared as follows. To atoluene solution (2 ml toluene/mg metallocene) ofethylene-bis-(4,5,6,7-tetrahydroindenyl)zirconium dichioride a toluenesolution of triisobutylaluminum (TIBAL) (0.2 g TIBAL/mi solution) wasadded. The mixture was kept under stirring at the temperature of 20° C.for 5 minutes, then the solution was injected in the autoclave underpression of ethylene/propylene mixture in such a ratio to maintain thecomposition constant in the reaction bath. The temperature was thenraised to the value requested for the polymerization. The polymerizationconditions are reported in Table 1. Fouling phenomena in the reactorwere not observed. The polymer obtained was separated by removing theunreacted monomers and thereafter dried under vacuum. Data relating tothe characterization of the polymer obtained are reported in Table 2. Inthe ¹³C-NMR no peak showing the presence of −(CH₂), sequences comprisedbetween tertiary carbon atoms, wherein n is an even integer, wasdetected.

EXAMPLE A (Comparison)

It was worked according to the procedure described in example 1, butwith a content of liquid 1-butene in the reaction mixture lower than thelowest limit according to the present invention. Polymerizationconditions are reported in Table 1. The polymer obtained appears as asingle mass packed in the reactor. Data relating to the characterizationof the polymer obtained are reported in Table 2.

EXAMPLE 4

It was worked according to the procedure described in example 1, but inthe absence of water and using methylalumoxane (MAO) instead of TIBAL.Polymerization conditions are reported in Table 1; Fouling phenomena inthe reactor were not observed. Data relating to the characterization ofthe polymer obtained are reported in Table 2.

TABLE 1 Zr Exam- (mmol Al Al/H₂O C₂ liquid phase C₃ liquid phase C₄liquid phase P tot. T time yield Activity ple 10⁻³) (mmol) (mol.)(grams) (weight %) (grams) (weight %) (grams) (weight %) (bar) (° C.)(min) (g) (Kg_(pol)/g_(Zr)) 1 1.875 1.875 2 174.6 13.19 500 37.76 694.449.05 23.5 50 60 126  736.8 2 1.875 1.875 2 196.0 15.55 700 55.51 364.828.93 27.8 50 60 244 1426.9 3 1.875 3.75  2 207.3 16.63 800 64.15 239.519.21 29.7 50 120  466 2725.1 COM- 1.875 3.75  2 228.8 17.9  900 70.3 151.1 11.81 31.3 50 60 141  824.5 PAR.A 4 0.937 1.875 — 207.3 16.63 80064.15 239.5 19.21 30.3 50 60  43  502.9

TABLE 1 Zr Exam- (mmol Al Al/H₂O C₂ liquid phase C₃ liquid phase C₄liquid phase P tot. T time yield Activity ple 10⁻³) (mmol) (mol.)(grams) (weight %) (grams) (weight %) (grams) (weight %) (bar) (° C.)(min) (g) (Kg_(pol)/g_(Zr)) 1 1.875 1.875 2 174.6 13.19 500 37.76 694.449.05 23.5 50 60 126  736.8 2 1.875 1.875 2 196.0 15.55 700 55.51 364.828.93 27.8 50 60 244 1426.9 3 1.875 3.75  2 207.3 16.63 800 64.15 239.519.21 29.7 50 120  466 2725.1 COM- 1.875 3.75  2 228.8 17.9  900 70.3 151.1 11.81 31.3 50 60 141  824.5 PAR.A 4 0.937 1.875 — 207.3 16.63 80064.15 239.5 19.21 30.3 50 60  43  502.9

What is claimed is:
 1. An elastomeric copolymer of ethylene containingfrom 35% to 85% by moles of ethylene units, from 10% to 65% by moles ofunits deriving from propylene and from at least one alpha-olefin offormula (I): CH₂═CHR  (I) wherein R is an alkyl radical containing from2 to 10 carbon atoms, and from 0 to 5% by moles of units deriving from apolyene, having the following characteristics: product of reactivityratios r_(e)·r_(α) lower than 1; less than 2% of CH₂ groups in thecopolymer contained in sequences (CH₂)_(n), wherein n is an eveninteger; and intrinsic viscosity higher than 3 dl/g.